The present invention relates to a component for a hydraulic braking system in an automotive vehicle and more particularly, to an electrically actuated valve device which can also provide a pump function.
Modern motor vehicles are increasingly equipped with anti-lock braking systems (ABS) and other similar braking torque control systems. ABS automatically relieve applied brake force to wheels experiencing a lock-up condition during braking, associated with skidding and loss of directional control. In addition to braking torque control, the components used in ABS are now being employed for other advantageous vehicle functions. For example, traction control systems (TCS) can apply braking torque to a spinning wheel to enable increased driving torque to be transferred to the opposite wheel through the vehicle's differential. TCS therefore involves applying braking torque while the operator is not depressing the brake pedal. In addition, automobile stability management systems (ASMS) apply braking torque to selected wheels while the vehicle is undergoing a turning maneuver to provide enhanced directional control in skidding conditions.
In the case of all the above described systems, which can be broadly described as electronic braking control systems, an active source of hydraulic fluid pressure, that is a pump, and a control valve system is used. The control valves, which modulate the application of fluid pressure to the wheel cylinder, are typically of the spool valve (or shuttle valve) variety. Depending on the vehicle application, the spools can be moved between positions by applied fluid pressure, or moved under the influence of external mechanical forces such as applied by an electrical solenoid.
Present spool type brake force valves act to control pressure by covering and uncovering ports through which fluid flows. Thus, they can be modeled as a single valve or a series of valves which are controlled simultaneously. The control functions are thus provided by creating various levels of restriction to the flow of brake fluid. These valves are not ordinarily capable of increasing fluid pressure or providing a pumping function of their own.
In certain designs of electronic braking control systems, there is a need to provide a brake force valve which further provides a pumping function. Even a pumping function of limited output capacity may aid in providing increased system transient response, enabling more rapid response by downstream connected devices, and providing a pressure spike where pressure from the system's pump is still building.
The present invention provides a brake force valve which provides a pumping function, to address the needs mentioned previously.